As is well known in the art, a peanut oil is produced by mechanically pressing and extracting oil from the pressed and crushed seeds. The peanut seeds which are to be thus processed for the production of a peanut oil have testae or skins containing tannin on their inner surfaces. The astringent content, tannin, of the peanut seeds has a bitter taste and an objectionable odor and is responsible for the tendency of the extracted oil to be oxidized when heated to a high temperature during the pressing and extracting procedures.
To provide a useful solution to such a problem, the inventor has developed an improved process of producing a peanut oil, the process being taught in Japanese Patent Application No. 49-122387 (now Japanese Provisional Patent Publication No. 51-49209). In the process disclosed therein, peanut seeds cleared of skins are immersed in a solution of salt for a predetermined period of time and are thereafter cooked in a dual-shell steam tank. The dual-shell steam tank must thus be coated with a special anti-corrosive lining and a subsequent high-pressure, high-temperature treatment. Since, furthermore, some organic and inorganic acids are used during separation of oil from a solid fraction in a separating bath, a neutralizing step must be taken to prevent corrosion of the separating bath and from the view point of food sanitation. Addition of such a step gives rise to an increase in the number of the steps of the process and further results in the grade the final product due to the existence of a neutralizing compound which may be left on the inner surfaces of the separating bath. The present invention contemplates provision of solutions to these problems encountered in prior-art processes of producing peanut oil.